A proportional timing generator for measuring intermodulation product distortion on television transposers.

Abstract:

Broadcasting authorities presently measure intermodulation distortion by
applying a three tone simulation of a composite video and sound signal to the
transposer and then measuring the relative amplitude of the major in-band
intermodulation product (nominally at vision carrier frequency plus 1,57 MHz in
the 625 line I/PAL System) on a spectrum analyser. This method is slow and
requires a skilful operator to achieve repeatable results. Furthermore it tests the
common RF amplification equipment at one luminance level and one
chrominance level and therefore does not subject the transposer equipment to
operation over its full range.
A new sampling measurement technique has been proposed which overcomes
all these problems by selectively mixing, while transmitting a colour bar test
pattern, the demodulated output video signal of the frequency transposer with
a pulse train coinciding with a particular colour. This thesis describes the
design of a very stable proportional timing generator and its application to the
measurement of intermodulation distortion on frequency transposers.
The timing generator, which locks automatically onto the video signal and
produces narrow sampling pulses which coincide accurately with a particular
section of each line over a 50°C temperature range, is applicable to all PAL and
NTSC TV Systems.